Crystal diode unit



June 1956 H. M. WADSWORTH CRYSTAL. DIODE UNIT Filed April 3, 1952INVENTOR. flown/d 772. Mdswvrlh BY MATT WITNESS United States PatentCRYSTAL DIODE UNIT Howard M. Wadsworth, Liverpool, N. Y.

Application April 3, 1952, Serial No. 280,410

Claims. (Cl. 317-236) The present invention relates to a crystal diodecapsule and more particularly to structure for supporting the electrodeof a crystal assembly in a sealing envelope or casing.

In crystal diode assemblies such as germanium crystal units as nowcommercially available, a tiny plate of crystal is rigidly mounted onthe end of a Wire electrode, and a cat whisker of very fine wire ismounted on the end of a similar electrode, and the electrodes arerigidly mounted and hermetically sealed in a tubular sheath or casing ofdielectric material such as a plastic tube, in such position that theend of the cat whisker rests on the surface of the crystal with apredetermined light pressure.

It is customary to make the sealing connection between the electrodesand the plastic tube by means of metal thimbles or ferrules which arecemented in the ends of the tube and are soldered to the electrodes.During the assembly of the parts it is desirable that the thimbles holdthe electrodes frictionally with sufficient security to maintain theiradjustment prior to and during the final sealing operation.

When it is considered that the external diameter of the electrodes isonly about .079 inch, and their longitudinal adjustment must be held towithin about .001 inch to maintain the pressure of the cat whisker onthe crystal within accepted tolerances, it is apparent that theprovision of thimbles having the requisite elasticity, stiffness andgrip on the electrodes, and security of attachment to the tubing so asnot to be loosened when the electrodes are inserted, presents a verydiflicult problem. Various forms of slotted or crimped thimbles havebeen tried, but none of them have been entirely satisfactory, due todifficulty in maintaining spacing and alignment of the electrodes,breakage, leakage etc.

It is an object of the present invention to provide a novel crystalassembly unit of which the parts are economical to produce and may beeasily assembled and sealed without loss of adjustment.

It is another object to provide such a device incorporating mountingthimbles for the electrodes which provide a plurality of axiallyextending line bearings spaced about the peripheries of the electrodesand gripping them with substantially uniform pressure throughout themajor portion of the length of the tubular casing.

It is another object to provide such a device in which the thimbles arefree from slots or sharp bends which would be conducive to localizedstresses and would render it difiicult to obtain a tightly sealedconnection.

Another object is to provide such a device in which the tubular casingis of vitreous material, and the thimbles are sealed in the ends of thetube by a fusing operation prior to the assembly of the electrodes.

Further objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawing in which:

Fig. l is a substantially mid-sectional view of a crystal unitconstituting a preferred embodiment of the invention 2,750,543 PatentedJune 12, 1956 on a highly enlarged scale, the electrodes being shown inelevation;

Fig. 2 is an end view of the unit shown in Fig. 1;

Fig. 3 is still further enlarged end view of a thimble;

Fig. 4 is a view similar to Fig. 3 of the opposite end of the thimble;and

Fig. 5 is a longitudinal section through a thimble.

In Fig. 1 of the drawing there is illustrated a cylindrical electrode 1on which a plate 2 of crystalline material such as germanium is fixedlymounted in any suitable manner. A second electrode 3 has a fine wire catwhisker 4 attached at one end thereto as by welding, the free pointedend of the cat whisker being arranged to contact the surface of thecrystal 2.

A hollow tubular casing 01'' envelope 5 of suitable material such asglass loosely surrounds the electrodes 1 and 3 and a pair of thimbles ornipples 6 and 7 are mounted in the ends of the casing 5 and support andseal the electrodes in the casing. Each thimble is provided on its outerend with a radial flange 8 which is rigidly mounted and sealed in theend of the casing 5, preferably by fusing the glass around the flange asshown at 9.

According to the present invention, these nipples are so formed as togrip the electrodes elastically throughout a considerable portion oftheir length by means of straight line bearings which hold theelectrodes in proper alignment and offer sufiicient resistance toendwise movement of the electrodes to prevent their shiftingaccidentally before or during the final sealing operation. For thispurpose, the skirts 11 of the thimbles which are originally cylindricalare distorted for a portion of their length as shown at 12 in Figs. 4and 5 by displacing longitudinal strips or panels of the skirt inwardly.As here illustrated three such panels or lands 12 are formed so that thesection of the skirt as deformed is roughly triangular in shape andsubstantially uniform for a major portion of its length as illustratedin Figs. 1 and 5, the panels or lands being connected by smoothly curvedoutwardly projecting portions 13 as shown in Fig. 4, whereby the panelscan flex radially altho the skirt is continuous and free from slits oropenings.

It will be understood that more than three strips or panels may beformed if desired, and the strips may be curved inwardly instead ofbeing fiat as illustrated.

The strips 12 extend inwardly to such an extent that a circle inscribedin a right section of the skirt is of slightly smaller diameter then thediameter of the electrodes. When an electrode is pressed into the nippletherefore it has a plurality of line contacts with the skirt which gripthe electrode firmly due to the elasticity of the curved portions 13 ofthe skirt.

In assembling the device, the two thimbles 6 and 7 are first fused intothe tube 5 while maintained in alignment on a suitable mandrel. Themandrel is then withdrawn, and the electrodes inserted by pressing themthrough the nipples until the cat whisker 4 engages the crystal 2 withthe desired amount of pressure. The units can then be handled withoutdanger of losing the adjustment of the cat whisker, by virtue of thestrong gripping engagement of the panels 12 of the skirts of thenipples.

The capsule is then finally sealed by soldering the throats of thenipples to the electrodes as shown at 14 in Fig. 1.

Although but one embodiment of the invention has been shown anddescribed in detail it will be understood that changes may be made inthe precise form and dimensions of the parts without departing from thespirit of the invention.

What is claimed is:

1. In a crystal diode assembly, a cylindrical electrode, a crystal platefixed on one end thereof, a second electrode, a spring Wire filamentattached at one end thereto; a hollow cylindricalcasing of dielectricmaterial, and a-pair of tubular'thimbles of elastic metallicmaterialextending into the ends of the casing, said thimbles having radialterminal flanges sealed to the ends of the casing, the bodies'of thethimbles being-formed -with-a =plurality of axially extending landsbetween which the "electrodes are firmly gripped, said land portions of'the thimbles being 'equidistantly spaced about the bodies of thethimbles, and the portions of said bodies btweenthe lands being smoothlycurved and adapted to' b'ear' f'rictionally throughout theirlength onthe" interior of the cylindrical casing.

2. In' an electricalcoupling'unit; a hollow cylindrical casing; 21 pairofhollow thimbles'h'aying 'radial fianges rigidly mounted -in the endsof the casing and tubular skirts which are continuous throughout -theirlength 'extending intothe casing, a cylindrical electrode attending intoeach end of the casing through said thirnb'les," each of "saidskirtsbeing distorted inwardly' for' -a-por'ti'on 'of-its length ata'-plurality=of circumferentially:spacedareas to form' axially extendingflattened panels, said' electrodes being frictionally held andmaintained in"alignment by line contact with said inwardly displacedareas of t-he skirt.

V 3. A crystal diode assembly as set forth in claim 1 in which thegripping portions of -the thimbles -extend tor-a major portion of thelengthrof the thimbles, with substantially uniform cross-section.

4. A crystal diode assembly as set forth in claim 1 in which the casingis formed of vitreous material, and the flanges of the elastic metallicthimbles are fused in the ends of the casing.

5. A unit as set forth in claim 2 in which the skirts of the thimblesengaging theelectro'des areof substantially uniform cross-section for amajorportion of their length, said panels being joined by smoothlycurved outwardly projecting-portions pei'rnit'ting l ra dia ffiexureofthe panels,

References Cit edin the file 'oflhis patent UNITED STATES PATENTS1,897,761 McCullough Feb. 14, 1933 72,180,665 Bruggerman 'Nov. 2-1, 19392 ,411,861 Antony et al.. Dec. 3, 1946 2 ,422,265 Squires June 17,19472,588,956 Britain et al. Mar. 11, 1952 FOREIGN PATENTS 404;505 GreatBritain Jan. its, 1914

